Travel through millions of years of history on the Fossil Discovery Trail. Long ago, dynamic forces pushed and tilted these layers of rock upward. Later, erosion exposed the layers as colorful ridges. Erosion also revealed remnants of ancient ecosystems including now-extinct animals that inhabited landscapes quite different from today. Sites on the Fossil Discovery Trail include the Stump Formation. 163 million years ago, this area was part of a large inland sea.

The Stump Formation reveals evidence of an ocean environment with a large variety of life. Fossils in these rocks include belemnites (squid-like sea creatures), snails, ammonites, and bones of an ichthyosaur (giant marine reptile that resembled a modern dolphin).

Another site, the Morrison Formation, which has rock layers with different colors, textures, and fossils. Sometimes these differences are subtle, sometimes striking. Most of the Morrison Formation is mudstone and clay, but there is a sandstone cliff. This part of the Morrison Formation is made up of river-deposited sand and gravel. Based on potassium-argon dating of volcanic ash, in older and younger layers on either side of the sandstone wall, this layer is estimated to be about 149 million years old. Fossil fragments of dinosaurs are embedded in the cliff along with impressions of freshwater clams.

The Morrison Formation trail spur follows the same sandstone layer that is exposed in the Quarry Exhibit Hall. However, this cliff has not been worked on by paleontologists to make the bones easier to see. The first fossils along the spur are fragments that are somewhat shiny and dark orange in color. Some have a spongy-looking interior which contained bone marrow. Their texture is generally smooth and their size ranges from ½ inch to 10 inches in diameter.

Credits and Sources:

“Fossil Discovery Trail Brochure,” National Park Service, http://www.nps.gov/dino/planyourvisit/upload/2013-Fossil-Discovery-Trail-Site-Bulletin-Final-for-vc-printing.pdf (accessed 23 June 2015).